1. Field of the Invention
The present invention relates to a one-port elastic wave resonator in which IDT electrodes are provided on a piezoelectric substrate. The present invention further relates to an elastic wave filter apparatus and a duplexer each including the one-port elastic wave resonator.
2. Description of the Related Art
As a resonator in a filter apparatus, a surface acoustic wave resonator has been widely used. “A Triple-Beat-Free PCS SAW Duplexer,” (IEEE Ultrason. Symp., pp. 67-70, 2012) discloses a one-port surface acoustic wave resonator including a serially divided type IDT electrode. In this one-port surface acoustic wave resonator, a first IDT electrode and a second IDT electrode are connected in series. In order to obtain the same impedance as that obtained in a case where a serially divided type IDT electrode is not used, the areas of the first and second IDT electrodes are large. This leads to reduction in energy density in the first and second IDT electrodes and the suppression of distortions generated by a nonlinear signal.
On the other hand, Japanese Unexamined Patent Application Publication No. 2004-320411 discloses a surface acoustic wave apparatus used to increase a thermal shock resistance. In this surface acoustic wave apparatus, two surface acoustic wave resonator portions are formed on a piezoelectric substrate. These two surface acoustic wave resonator portions are connected in parallel. That is, a first IDT electrode forming a first surface acoustic wave resonator portion and a second IDT electrode forming a second surface acoustic wave resonator portion are electrically connected in parallel.
With the surface acoustic wave apparatus disclosed in “A Triple-Beat-Free PCS SAW Duplexer,” (IEEE Ultrason. Symp., pp. 67-70, 2012), it is possible to reduce nonlinear distortions. However, since the areas of the first and second IDT electrodes are large, it is difficult to achieve size reduction.
On the other hand, in the surface acoustic wave apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2004-320411, in order to increase a thermal shock resistance, a parallel connection structure is employed. With this structure, it is possible to suppress nonlinear distortions without increasing the areas of IDT electrodes. However, in the parallel connection structure disclosed in Japanese Unexamined Patent Application Publication No. 2004-320411, a routing line for connecting the first and second IDT electrodes takes up a lot of space. It is therefore difficult to achieve miniaturization.